
These include attics* and crawl spaces. Follow the National Fuel Gas Code NFPA 54/ ANSI Z223.1, Section 5.3, Air for Combustion and Ventilation for required size of ventilation grills or ducts. *IMPORTANT: Do not provide openings for inlet or outlet into attic. If attic has a thermostat-controlled power vent, heated air entering the attic will activate the power vent. IMPORTANT: Vent-free heaters add moisture to the air. Although this is beneficial, installing heater in rooms without enough vent